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Item Bubble dynamics of water-ethanol mixture during subcooled flow boiling in a conventional channel(Elsevier Ltd, 2017) Suhas, B.G.; Sathyabhama, A.In this paper, bubble dynamics in subcooled flow boiling of water-ethanol mixture in horizontal rectangular channels is investigated through visualization. The subcooled flow boiling heat transfer coefficient of water ethanol mixtures are determined for various heat flux, mass flux and ethanol volume fraction. A new empirical correlation is proposed to predict the heat transfer coefficient of pure water based on the parameters like heat flux, bubble departure diameter, waiting period and the growth period. Two types of bubble behaviours are observed after nucleation: (i) Sliding for a distance along the bottom wall of the channel surface before lift-off and (ii) Lift-off from the bottom wall of the channel surface without sliding. Force balance analysis is carried out to determine the reason for bubble lift-off and bubble sliding. The bubble lift-off without sliding is observed at higher ethanol volume fraction, lower heat flux and higher channel inlet temperature. The bubble sliding and lift-off are observed at higher heat flux and lower channel inlet temperature for water and water-ethanol mixture of 25% ethanol volume fraction. However, the effect of mass flux on the bubbles sliding or bubble lift-off is not significant. © 2016 Elsevier LtdItem Augmentation of heat transfer coefficient in pool boiling using compound enhancement techniques(Elsevier Ltd, 2017) Sathyabhama, A.; Dinesh, A.Modern compact electronic chip design demands more efficient and innovative cooling techniques in a limited space. One such method is the immersion cooling by pool boiling heat transfer, which is a highly efficient technique when compared with conventional cooling techniques. The boiling heat transfer coefficient can be enhanced using active and passive techniques. In the present investigation grooves as passive and surface vibration as active techniques were coupled to improve the boiling heat transfer coefficient. The forced vertical vibrations were induced on the copper grooved surface with a mechanical vibrator. The frequency of vibration was varied in the range 0–100 Hz and the amplitude of vibration was varied in the range 0–2.5 mm. The compound technique gave 62% improvement in heat transfer coefficient at 300 kW/m2 heat flux compared to the 29% enhancement due to grooves alone and 10% enhancement due to vibration alone. The experimental results were used to develop a modified Rohsenow correlation which predicts the experimental Nusselt number with an accuracy of ±25%. Boiling visualization was performed and the bubble parameters such as bubble departure diameter, bubble frequency and bubble growth were determined. The bubble departure diameter decreased by almost 36% and the bubble frequency increased by 221% for boiling on vibrated grooved surface. © 2017 Elsevier Ltd